I want to attach a drawing (say A.dwg) and want to query some objects from it and want to draw in the current drawing. In addition to that I also want to set the coordinate system of current drawing ,same as attached drawing(A.dwg). Can anybody tell me ,How can I do it by using C#(Arx).
It sounds like you are doing AutoCAD Map 3d stuff. Yes, you can programmatically do what you asked.
Have you downloaded AutoCAD Map 3d ObjectARX SDK? It comes with some Map 3d specific .NET samples, including doing attaching drawing and querying..
You might also want to search posts and post your question in AutoCAD Map 3d Developer forem here: